[Bug 111140] Buffer corruption with Chromium on gnome-shell (wayland) after taking a screenshot

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111140

--- Comment #15 from Jonas Ådahl <jadahl at gmail.com> ---
(In reply to Lionel Landwerlin from comment #14)

...

> I could image we could allow glGet*Image* in the driver but that would
> essentially be replicating what you would otherwise do in the application
> (e.g. blit to an offscreen buffer and read that one back).

FWIW, OES_EGL_image_external (used with EGLStreams) has similar limitations.
Other than that, from a Wayland buffer point of view, there are other things
that mandate drawing via an offscreen to get usable output (buffer transforms,
viewports etc), so it's not like there shouldn't be paths in the application
that handles these kind of situations either way.

> 
> The problem is that the driver does a bunch of tracking on what you do with
> the texture and puts it in the most sensible disposition for what it's used.
> Once that goes out of sync with what the other processes have, we're in
> trouble.

I don't think it's worth the trouble to let the driver handle if it would just
complicate things.

> 
> > 
> > Either way, I created
> > https://gitlab.gnome.org/GNOME/mutter/merge_requests/687 that should avoid
> > reading directly from it. It didn't reproduce with or without it, so if
> > anyone that can reproduce it can give it a test I'd appreciate it.
> 
> That fixes the problem on my side too. Thanks!

Thanks for testing! Thanks to Olivier too :)

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